Ag/MnO2 Composite Sheath-Core Structured Yarn Supercapacitors

Ji Hwan Kim,Mônica Jung De Andrade,Changsoon Choi,Jae Myeong Lee,Seon Jeong Kim,Ray H Baughman

doi:10.1038/s41598-018-31611-2

Abstract

One-dimensional (1D) yarn or fiber-based supercapacitors that have small diameter, volume and high mechanical strength are needed due to the demands on power source for wearable electronics, micro-devices, and implantable medical devices. The composite sheath is fabricated on a commercially available CNT yarn substrate by alternating depositions of MnO2 and Ag layers. Synergistic effect of high loading level of pseudocapacitive MnO2 and reasonably improved rate-capability are achieved. In the composite sheath, the interconnected networks provide electrical contact between MnO2 aggregates and adjacent Ag layer. The conductive Ag inter layers shorten the solid-state charge diffusion length in the MnO2. Moreover, generated electrons during the charge/discharge process can be collected rapidly by the adjacent Ag layer, therefore, the great extents of MnO2 could be loaded onto the surface of CNT core fiber electrode without a significant rate-capability degradation. Due to the high MnO2 loading level, the composite sheath-core yarn supercapacitor showed excellent specific areal capacitance (322.2 mF/cm2) and according energy density (18.3 µWh/cm2).

Highlights

One-dimensional (1D) yarn or fiber shaped micro-supercapacitors that possess small diameter, volume and high mechanical degree of freedom, like flexibility or stretchability are highly needed due to the sudden high demand on appropriate power source for wearable electronics, micro-devices, and implantable medical devices[1,2,3,4,5,6,7,8,9,10]
We introduce a novel composite sheath structured yarn supercapacitor, which consists of electrochemically active MnO2 and electrically conductive Ag
Generated electrons during the discharging process can be effectively collected by the adjacent Ag layer, the great extents of MnO2 could be loaded onto the surface of CNT core yarn electrode without a significant rate-capability degradation or an impediment of mechanical flexibility

Summary

Introduction

One-dimensional (1D) yarn or fiber shaped micro-supercapacitors that possess small diameter, volume and high mechanical degree of freedom, like flexibility or stretchability are highly needed due to the sudden high demand on appropriate power source for wearable electronics, micro-devices, and implantable medical devices[1,2,3,4,5,6,7,8,9,10]. As one of the promising pseudocapacitive active materials, MnO2 has been extensively studied due to its high theoretical energy storage capability, low cost, and environmental friendliness It has a poor electrical conductivity[14], which significantly limits the solid-state charge transport and leads to a significant performance degradation when the MnO2 loading density increases[15]. For storage performance resulting from high active material loading, thick and bulk pseudocapacitive sheath formation is needed onto the current collector It leads supercapacitors’ degraded rate-capability or specific power, and inhibition of solid-state charge diffusion process[14]. The composite sheath supercapacitor exhibited enhanced rate-capability, which is about 40% of the initial capacitance, and was retained when scan rate increased from 10 to 100 mV s−1, which is two-fold higher than pristine MnO2 sheath-core structured supercapacitor

Methods

Results

Conclusion